The present invention relates to method of adapting mixtures for internal combustion engines having direct gasoline injection.
It is conventional in the regulation of the fuel/air ratio of internal combustion engines to superimpose a pilot control including a regulation. It is further conventional that additional correcting quantities may be derived from the behavior of the regulating quantity to compensate for faulty adaptations of the pilot control to modified operating conditions. This compensation is also referred to as adaptation. U.S. Pat. No. 4,584,982 describes, for example, an adaptation with different adaptation quantities in various ranges of the load/speed spectrum of an internal combustion engine (range adaptation). The various adaptation quantities are directed toward compensation for different errors. Three types of errors may be distinguished, according to their cause and effect: errors of a hot film air flow sensor, which have a multiplicative effect on the fuel metering; air leakage influences, which have an additive effect per unit of time; and errors in the compensation of pickup delays of injection valves, which have an additive effect per injection.
Under regulatory requirements, errors pertaining to exhaust gas emissions must be detected by an onboard arrangement, optionally with the activation of a malfunction light. Mixture adaptation is also used for fault diagnosis. An error is indicated if, for example, the corrective intervention of the adaptation is too great.
Over the operating life, for the manufacturing tolerance and during unregulated sensor heating, the measured lambda value deviates from the lambda value which is physically present, primarily in the stratified charge mode in engines having direct gasoline injection.
Since the mixture adaptation takes the measured lambda into account for error learning, the adaptation in stratified charge mode does not lead to the desired result. For the adaptation, therefore, the operation is switched to homogeneous mode and mixture adaptation is activated.
An engine control program is described in German Published Patent Application No. 198 50 586 which controls switching between stratified charge mode and homogeneous mode.
In stratified charge mode, the engine is operated with a highly stratified cylinder charge and high excess air to obtain the lowest possible fuel consumption. The stratified charge is achieved by delayed fuel injection, which ideally results in a division of the combustion chamber into two zones, with the first zone containing a combustible air-fuel cloud mixture at the spark plug. The first zone is surrounded by the second zone which includes an insulating layer composed of air and residual gas. Consumption may be optimized by operating the engine largely unthrottled while avoiding charge exchange losses. The stratified charge mode may be preferred at comparatively low load.
At higher load, when optimization of performance is of chief importance, the engine is operated with homogeneous cylinder filling. Homogeneous cylinder filling results from early fuel injection during the intake process. Consequently, there is more time for forming a mixture up to the point of combustion. Performance may be optimized in this mode of operation, for example, by making use of the entire volume of the combustion chamber for filling with the combustible mixture.
Several starting conditions are necessary with regard to adaptation:
For example, the engine temperature must have reached the starting temperature threshold, and the lambda sensor must be ready to operate. In addition, the current values of load and rotational speed must be arranged in specific ranges in which learning occurs. This is described in U.S. Pat. No. 4,584,982, for example. Furthermore, the operation must be in homogeneous mode. According to the conventional program, the switching from stratified charge mode to homogeneous mode is independent of whether an error is present in the system.
It is an object of the present invention to increase the time period in which the engine is capable of being operated in stratified charge mode with optimum consumption. Switching to homogeneous mode for diagnosis may reduce the consumption-related advantages of direct gasoline injection, since homogeneous mode may be more unfavorable for consumption than stratified charge mode. Switching to homogeneous mode therefore may unnecessarily increase the fuel consumption when an error is not present. Switching to homogeneous mode may thus be avoided to the greatest extent possible without compromising the detection of exhaust gas-related errors.
A method is described to compensate for faulty adaptations of the pilot control of fuel metering (adaptation) for an internal combustion engine which is operated in the at least two different operating modes, homogeneous mode and stratified charge mode, with mixture regulation and adaptation of mixture regulation occurring in homogeneous mode, with switching occurring between the operating modes, as a function of a desired operating mode which is determined from a plurality of operating mode requirements, each of the operating mode requirements being assigned a priority, with the desired operating mode being determined depending on the priorities of the operating mode requirements, with switching to homogeneous mode with the activation of a temperature-dependent adaptation momentarily occurring, even outside the normal starting conditions of a range-dependent adaptation, and with a deviation of the magnitude of adaptation from its neutral value during the short-time activation of the temperature-dependent adaptation being evaluated as a suspected error, and with the engine control program raising the priority of the range-dependent adaptation under normal starting conditions when a suspected error is present.
An example embodiment may provide that the short-time mixture adaptation is activated below the minimum temperature of the range-dependent adaptation.
A further example embodiment may provide that the minimum temperature of the range-dependent adaptation is equal to or greater than 70xc2x0 C.
A further example embodiment may provide that the short-time mixture adaptation is activated for a period of time in the range of approximately 10 to 20 seconds.
A further example embodiment may provide that the physical priority is canceled if the error has been learned in the normal range-dependent mixture adaptation, so that the range-dependent mixture adaptation is enabled at normal priority by the engine control program.
A further example embodiment may provide that the value of the temperature-dependent short-time adaptation is maintained when the motor vehicle is parked, and during the initialization phase, after the next time the engine is started, it is set back by the value learned within the scope of normal range-dependent mixture adaptation.
A further example embodiment may provide that the operating parameter-dependent (range-dependent) mixture adaptation has a multiplicative and/or additive effect on the fuel metering.
A further example embodiment may provide that the value or values of the range-dependent adaptation are renewed above a temperature threshold and have an effect on the fuel metering independent of temperature.
A further example embodiment may provide that the deviation of the instantaneous temperature-dependent adaptation factor is derived from a long-term adaptation factor to form the suspected error.
The present invention is also based on an electronic control device for performing at least one of the aforementioned methods and example embodiments.
One aspect of the present invention is a short-time mixture adaptation which occurs even outside the normal starting conditions of the adaptation, e.g., below the minimum temperature of the range-dependent adaptation. According to the present invention, the short-time mixture adaptation is activated only for a very short period of time, in the range of approximately 10 to 20 seconds. If an error is present, the magnitude of the correction of the short-time temperature-dependent adaptation deviates from its neutral value.
According to the present invention, the deviation raises the priority of the normal mixture adaptation within the scope of the operating mode control program. If the operating conditions of the normal mixture adaptation are then satisfied, the normal mixture adaptation is started relatively quickly.
If the error has been learned in the normal range-dependent mixture adaptation, the physical priority is canceled, with the result that the range-dependent mixture adaptation operates only when it is enabled at normal priority by the engine control program.
Since the value of the temperature-dependent short-time adaptation is maintained when the motor vehicle is parked, and is incorrect the next time the engine is started, again in the de-adapted state, the temperature-dependent short-time adaptation is set back during the initialization phase, after the next time the engine is started, by the value learned within the scope of normal range-dependent mixture adaptation.
This may provide the advantage that in the non-adapted state the physical priority of the normal adaptation immediately increases.
Since the temperature-dependent adaptation may provide only a 3 to 4% correction in the normal state, the maximum of the integrator is corrected downward or upward, depending on the learned error, so that, for example, for a 20% error learned only a 5% correction is permitted.
In the error-free state, switching to homogeneous mode occurs only in large time intervals. In the error state of a cold engine, the time intervals during the operation are at first very short, and then long. If no error has been learned, the short time intervals are repeated after the engine starts. If an error is learned, operation occurs in homogeneous mode, once again in long time intervals. In the method according to the present invention, switching to homogeneous mode, which may be less favorable for consumption, is performed only very briefly, and for suspected errors, the temperature-dependent mixture adaptation is activated immediately. If no error is present in the system, the mixture adaptation is activated less frequently, so that the time period in which the engine is capable of being operated in stratified charge mode with optimal consumption is extended.